package pers.qianyu.month_202011.date_20201111;

/**
 * 面试题 08.01. 三步问题
 * https://leetcode-cn.com/problems/three-steps-problem-lcci/
 *
 * @author mizzle rain
 * @date 2020-11-11 22:13
 */
public class WaysToStep {
    public int waysToStep(int n) {
        if (n == 1) {
            return 1;
        }
        if (n == 2) {
            return 2;
        }
        if (n == 3) {
            return 4;
        }
        int[] dp = new int[n + 1];
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 4;
        for (int i = 4; i < dp.length; i++) {
            dp[i] = (dp[i - 1] + dp[i - 2]) % 1000000007;
            dp[i] = (dp[i] + dp[i - 3]) % 1000000007;
        }
        return dp[dp.length - 1];
    }
}
